This application claims the priority of German application 197 33 473.3, filed Aug. 2, 1997 in Germany, the disclosure of which is expressly incorporated by reference herein.
The present invention concerns a process for producing a linkage or connection between a hollow cylindrical air/fuel ratio detector holder and an exhaust pipe which acquires a desired finished shape through internal high-pressure forming or xe2x80x9cremodelingxe2x80x9d of a blank piece, and a device or apparatus for carrying out the process.
Air/fuel ratio detector holders are known in manifold types, as shown for example, in DE 34 09 045 C1. In all of these known configurations, the holder is fitted specifically to the curved shape of the exhaust pipe in order to attain a dimensionally stable link between the holder and the exhaust pipe. This guarantees that a subsequent welding of the holder to the exhaust pipe creates a connection which withstands mechanical and thermal stress. The specific fitting process is, however, expensive in terms of production technology and is thus cost-intensive. In particular, in tight component space conditions, in which the hollow cylindrical holder is forced to be fastened with its casing to the exhaust pipe, this can be accomplished accurately only either through a highly complicated contour milling of the casing of the holder, or through forming the holder as a precision cast part whose contour structure is shaped during the casting procedure. Both methods demand expensive tools and involve long processing times. This also causes increased costs in the shaping of an appropriate link between the holder and the exhaust pipe.
An object of the present invention is to provide a process or respectively a device with which a dimensionally stable link or connection is attained between an air/fuel ratio detector holder and an exhaust pipe, in a simple manner and by saving space for the components.
This object has been achieved in accordance with the present invention by a process in which a contact surface formed by a buckling portion of the exhaust pipe has an inverted shape of the contact contour of the holder casing surface. A device for effecting this process includes a tool with an upper and lower die for xe2x80x9cremodelingxe2x80x9d or forming an inserted blank pipe into the desired shape of the exhaust pipe. The remodeling tool integrated shaping apparatus has a contour facing the blank pipe and corresponds to the contact contour of the holder casing surface.
The present invention is based on the recognition that it is advantageous to use an internal high-pressure technique for the shaping of the link to shape exhaust pipes with essentially tolerance-free complicated curvatures as exhaust pipes or their parts are so manufactured increasingly in recent times. With this, in a simple manner, the exhaust pipe is shaped with internal high pressure at the point where the future contact surface of the holder is planned to be, true to form with regard to the contact contour of the casing of the holder in inverted shape. The link of the holder with its casing to the exhaust pipe saves space for components, as the holder has at this point a certain circumference sunk, so to speak, into the exhaust pipe, or at least however flush with the pipe side. This takes place in the production in only one operation, jointly with the remodeling or forming of the blank pipe into the desired finished shape of the exhaust pipe.
An added benefit of the process of the present invention is that the shaping of this link can be exactly reproduced over many forming or remodeling operations. In addition, this approach eliminates both the need for developing expensive special parts, such as the in the aforementioned precision-cast part, and costly special production processes, which are suitable for fitting the holder to the exhaust pipe in the contact contour.
Now, with the present invention, only a simple and cost advantageous frame or body is needed as holder, which in addition to the internal thread for the accommodation of the screw of the air/fuel ratio detector need have only a transverse bore which corresponds to the opening in the exhaust pipe configured to provide access for the exhaust stream to the air/fuel ratio detector. In addition, the joint or shared use of the same tools appears advantageous in terms of cost savings and expenditure of space. The shaping apparatus can be installed permanently in a matrix or body of the remodeling tool or integrated into a substitutable body which can be introduced into the remodeling tool whenever required.